Bath tub insert



FIG. 1 is a left side elevational view of a bath tub insert showing my new design; the right side being a mirror image of the left side;

FIG. 2 is a front end elevational view view thereof;

FIG. 3 is a rear end elevational view thereof;

FIG. 4 is a top plan view; and,

FIG. 5 is a bottom plan view thereof. 

The ornamental design for a bath tub insert, as shown and described. 